The technique of the mural paintings of the Tournai Cathedral

Studies on mural paintings from the Tournai Cathedral (Belgium) were carried out by micro-Raman spectroscopy. The analyses were performed on micro-samples extracted from the remaining paintings and architectonic decorations, and concerned the pigments, the binders and, in some case, the stratigraphy. The palette was established and various pigments were identified, according to the Romanesque and Gothic periods. Red color was largely made of iron oxides. Lapis lazuli was also found in abundance, mainly on the areas that are assigned by historians to the Romanesque period. The green pigments revealed the use of atacamite and posnjakite. It was also found that some of the paint layers were applied using egg yolk as binding medium. These layers cover the stone above a very thin coating made of gypsum and chalk. The presence of oxalates was often noticed. This can be related to aging due to degradation of chalk by aggressive lichen, but also as result of a degradation of organic substances applied during past restorations. The gypsum is also altered by partial or complete dehydration, thereby damaging the artwork on which the painting is based. In humid conditions, iron oxide could be transformed in its hydrolyzed counterpart, whose Raman spectrum was often observed. Finally, a stratigraphic analysis was carried out on a multilayer fragment from the outside whitewash of the Cathedral, and despite a clear visual difference in morphology, each layer showed surprisingly the same chemical composition. Copyright (C) 2006 John Wiley & Sons, Ltd.